Humless electrodynamic pickup



Feb. 18, 1947. BALMER HUM-LESS ELECTRODYNAMIC PICKUP Filed Aug. 8, 1944 2 Sheets-Sheet l r Rm Y a o E V.. T 5. 1: i A m aw fl ic z a Feb. 18, 1947. BALMER 7 2,416,082

HUM-LESS ELECTRODYNAMI C PICKUP Filed Au fa, 1944 2 Shegts-Sheet 2 j I INVE NTOR Jon alcZEBaZ'mer ATT-ORNEY 3 '29 (see Ri 5).

screw rod l6,

gaging recesses 26, 21 which tightly embrace the The intermediate portion of the rear cushion member 23 is provided with a horizontal central slit 28 which is adapted to receive a thin reduced rear horizontal end lug 3| on the Lucite frame The numeral 3 2 indicates a cylindrical stylus rod which is adapted to be vibrated laterally by The disk record 34 recording machine such as was disclosed in the Reissue'Patent No. 22,183, issued to Lincoln Thompson, on' Sept. 22, 1942, and entitled "Appa- 1 I ratus for recording sound on thin disks.

The numeral 38 indicates a central iron core,

about which is wound a moving coil 31, said core I being movable with said coil 31 and filling the 1 entire space therein without air gaps.

The Lucite frame 29 has an intermediate upwardly opening recess 36, a thin rear vertical j section 39, and a thick forward vertical section 40', the combined moving coil 31 and core 38 being tightly cemented between the sections 39, 40 of said Lucite frame 29, as best shown in Fig. 6. Provision is also made of a rectangular top fiat .fibrestrip 4| cemented to the top of the pole pieces I3, l4 and having aninclined side section 42 upon which is mounted an elongated humbucking coil 43, the inclination of which'may be adjusted manually by bending sald'side section 42 with respect to the strip 4| until the hum produced by the lines of force of a stray ma netic-field S. Fpemanating' from a turntable motor 4311 (Fig. 11) or other sourceof electrical disturbances has been compensated for. The hum-bucking coil 43 is providedwith a central iron core 44 similar to the core 38.

It will beunderstood from the above construc- 1 tion that by placing the stationary hum-bucking coil 43 in close proximity to the driven moving pickup con 31 in such a position that both coils will be affected .by the same disturbing stray fields it will only be necessary to'conn'ect the coils v in opposition so as to substantially eliminate all hum and other undesired disturbing noises.

ments of the rear of the pickup armature A, which might cause gurgling noises, provision is made of. an elongated transverse brass wire 45 having a downwardly bowed central portion 46 which engages the rear .armature cushion mem ber'23, the ends 5|); 5| of said wire 45 being rigidly secured to the frame members I I, I2 as by cement,

as shown.

I 7 moving coil 31 which would not be equal in "all directions, as in- Fig.7 9, but would be unbalanced since the axis of such vertical motion would be inclined as indicated in an exaggerated manner by the line 48 in Fig. 10. This would result in the production of gurgling noises unless the 'In order to prevent undesired-vertical move clamped upon opposite faces of'said block, said 2 vertical movements of the: rear"v of the pickup armature were suppressed. I

- An' additional function of the bentwire 45 is 'fication one form in which the invention may be embodied, it is to be understood that this form r a is shown for the purpose of illustration only, and

that the inventionis notto be limited tothe specific disclosure, but may be modified and embodied in various other forms without departing from its spirit.- In short, the invention includes all the modifications and embodiments coming within the scope of the following claims,

Having thus fully described the invention, what is claimed as newand for which it is desired to secure Letters, Patent, is:

- 1, In an electrodynamic pickup for reproducing 7 sounds from the grooves of a phonograph record, 7

a rectangular permanent magnet block, a pair of Z-shaped magnetic frame member clamped upon opposite faces of said block, said frame members having a pair of closely spaced inwardly offset pole pieces, a moving armature located in the air gap between said pole pieces and carrying a pickup coil, a stylus rigidly connected to said armature, yieldable cushions for the front and rear of said armature, and means secured to said frame to engage the cushion at the rear of said armature to restrain the latter from vertical movement wherebysubstantially any tendency to produce gurgling will be prevented.

2. In an electrodynamic pickup for reproduc-' ing sounds from the grooves of "a phonograph record, a rectangularpermanent. magnet block, a pair of- Z-shaped magnetic frame members clamped upon opposite faces of said block, said frame'members having a pair. of closely spaced inwardly offset pole pieces, a light weight elon-- gated rigid moving armature resiliently supported at its sends in a' pair of soft rubber pads carried by said magneticframe members at the front and rear thereof,.and means mounted in said frame to engage the rear pad to restrain the rear of said armature from vertical movement whereby substantially any tergency to produce ord, a rectangular permanent magnet block, a 7

pair of magnetic frame members embracing said block, said frame members having a, pair of closely spaced inwardly offset pole pieces, a pickup-carrying moving armature located in the air gap between saidpole pieces, a'stylus connected with said armature, a yieldable cushion mounted in said frame members for resiliently receiving the'forward portion of saidarmatureto permit'it to vibrate with said stylus, and a curved wire member for holding the rear'of said armature to prevent vertical movements thereof and thus prerecord, a rectangular permanent magnet block, a,

pair of Z-shaped magnetic frame members frame members having a pair' of closely spaced inwardlyoffset pole pieces, a pickup coil carrying moving armature located in the air gap between said pole pieces, a stylus connected with said armature, and a curved brass wire member secured to the outer portions of said frame members for holding the rear of said armature from undesired vertical movements.

5. In an electrodynamic pickup for reproducing sounds recorded in a laterally undulated groove of a phonograph record, a magnetic frame having a pair of pole pieces separated by an air gap, a pickup armature located in said air gap and carrying a, stylus which rides in said groove and is vibrated laterally thereby, and additional means secured to said frame to restrain the rear of said pickup armature from undesirable vertioal vibrations around axes at right angles to the axis of its lateral stylus vibrations whereby any tendency to produce gurgling will be p1evented.

6. In an electrodynamic pickup for reproducing sounds from a laterally undulated groove of a phonograph record, a magnetic frame having a pair of poles separated by an air gap, a pickupcarrying movable armature located in said air gap, a yieldable rear cushion member mounted in said frame, said cushion member having a slit for resiliently embracing the rear of said armature, and means to press downwardly upon the top of said cushion to hold said slit closed .to prevent erratic movements of the rear of said armature.

DONALD F. BALMER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,213,936 Thompson Sept. 3, 1940 2,290,057 Lindenberg July 14, 1942 2,148,796 Barbieri Feb. 28, 1939 2,105,167 Sinnett Jan. 11, 1938 2,275,309 Norton Mar. 3, 1942 FOREIGN PATENTS Number Country Date 416,574 British Sept. 13, 1934 396.875 British Aug. 17, 1933 

